1. Field of the Invention
The present invention relates to an electromagnetic interference shielding filter and a manufacturing method thereof, in which the surface of an electromagnetic interference shielding layer is melanized (or blackened) to improve contrast ratio.
2. Discussion of the Background Art
In general, image display devices have an electromagnetic interference (EMI) shielding filter on the front surface to shield emission of electromagnetic waves to outside. The EMI filters not only shield electromagnetic waves but also transmit visible rays, so they usually have a conductive mesh pattern. A related art conductive mesh pattern, however, reflected an external light or a visible ray from a display panel. As a result, contrast was deteriorated. This problem is apparent in a plasma display panel (hereinafter it is referred to as “PDP”) that displays images by using a gas discharge.
PDPs regulate gas discharge time of each pixel on the basis of digital video data, and display an image. Typical examples of these PDPs are AC PDPs, as shown in FIG. 1, which includes three electrodes and are driven by an AC voltage.
FIG. 1 is a perspective view of a related art AC PDP. More particularly, FIG. 1 illustrates the structure of a discharge cell corresponding to a sub-pixel.
As shown in FIG. 1, the discharge cell is divided into an upper plate 15 and a lower plate 25. The upper plate 15 includes an upper substrate 10 where a sustain electrode pair 12A and 12B, an upper dielectric layer 14, and a protective film 16 are formed in sequence. The lower plate 25 includes a lower substrate 18 where an address electrode 20, a lower dielectric layer 22, a barrier rib 24, and fluorescent layers 26.
The upper substrate 10 and the lower substrate 18 are spaced out in parallel by the barrier rib 24. The sustain electrode pair 12A and 12B respectively includes a transparent electrode for transmitting visible rays, and a metal electrode for compensating resistance of the transparent electrode. The transparent electrode is relatively wider than the metal electrode. The sustain electrode pair 12A and 12B includes a scan electrode 12A and a sustain electrode 12B. The scan electrode 12A provides scan signals for determining data supply time, and sustain signals for sustaining the gas discharge. On the other hand, the sustain electrode 12B mainly provides sustain signals for sustaining the discharge. The upper dielectric layer 14 and the lower dielectric layer 22 are piled up with charges from the gas discharge. The protective film 16 protects the upper dielectric layer 14 from damages caused by a sputtering of plasma and thus, extends lifespan of the PDP and improves the emission efficiency of secondary electrons. The protective film 16 is usually made from magnesium oxide (MgO). The dielectric layers 14 and 22 and the protective film 16 lower an externally applied discharge voltage. The address electrode 20 is formed at right angles to the sustain electrode pair 12A and 12B. The address electrode 20 provides data signals for selecting cells to be displayed. The barrier rib 24 together with the upper and lower substrates 10 and 18 create a discharge space. The barrier rib 24 is formed in parallel with the address electrode 20, and prevents ultraviolet rays generated by the gas discharge from being leaked to the adjacent discharge cells. The fluorescent layer 26 is applied to the surface of the lower dielectric layer 22 and barrier rib 24, and generate one of visible rays in red, blue, or blue. The discharge space is filled with different compositions of inert gas mixtures including He, Ne, Ar, Xe, and Kr, or Excimer gas for generating ultraviolet rays.
Thusly structured discharge cell is selected by an opposing electrode discharge between the address electrode 20 and the scan electrode 12A, and sustained by a surface discharge between the scan electrode 12A and the sustain electrode 12B. Therefore, the fluorescent layer 26 is excited by ultraviolet rays generated during the sustain discharge, and visible rays are emitted to the outside of the cell. In this case, the discharge cell controls the cell's discharge sustain period, namely frequency of the sustain discharge, according to video data, and emits a light at a gray scale level.
FIG. 2 is a schematic perspective view of a PDP set including the PDP 30 of FIG. 1.
As shown in FIG. 2, the PDP set includes a case 60, a printed circuit board 50 (hereinafter, it is referred to as “PCB”) housed in the case 60, a PDP 30, a glass type front filter 40, and a cover 70 connected to the case 60 and encompassing the glass type front filter 40.
As discussed before with reference to FIG. 1, the PDP 30 includes an upper plate 15 and a lower plate 25 connected to the upper plate 15.
The PCB 50 disposed on the rear surface of the PDP 30 includes a plurality of driving and control circuits for driving the sustain electrode pair 12A and 12B and the address electrode 20 formed on the PDP 30. Situate between the PCB 50 and the PDP 30 is a heat radiation plate (not shown) for radiating heat emitted from the PDP 30 and the PCB 50.
The glass type front filter 40 shields electromagnetic waves generated from the PDP 30 towards the front surface, prevents external light reflection, blocks near-infrared rays, and corrects colors. To this end, the glass type front filter 40 includes, as shown in FIG. 3, a first antireflection coating 44 attached to a front surface of a glass substrate 42, an EMI shielding filter 46, a NIR (near infrared ray) blocking film 48, a color correcting film 52, and a second antireflection coating 54, the EMI shielding film 46, the NIR blocking film 48, the color correcting film 52 and the second antireflection coating 54 being layered in cited order on the rear surface of the glass substrate 42.
The glass substrate 42 is made from a reinforced glass to support the glass type front filter 40 and to protect the front filter 42 and the PDP 30 from damages caused by external impacts. The first and second antireflection coatings 44 and 54 prevent incident light rays from outside from being reflected back to the outside and thus, improve contrast effects. The EMI shielding filter 46 absorbs electromagnetic waves generated from the PDP 30, and shields the emission of the electromagnetic waves to outside. The NIR blocking film 48 absorbs near infrared rays at a wavelength band of 800-1000 nm that are generated from the PDP 30, and blocks the emission of the near infrared rays to outside. This is how infrared rays (approximately 947 nm) generated from a remote controller are normally input to an infrared ray receiver built in the PDP set. The color correcting film 52 contains a color dye, which is used to adjust or correct colors, whereby color purity can be improved. These films 44, 46, 48, 52, and 54 are adhered to the glass substrate 42 through an adhesive or glue.
The case 60 protects the PCB 50, the glass type front filter 40 and the PDP 30 from external shocks, and shields electromagnetic waves emitted from side and rear surfaces of the PDP 30. Also, to ensure that the glass type front filter 40 is separated from the PDP 30, the case 60 is electrically connected to the EMI shielding filter 46 of the glass type front filter 40 through a support member (not shown) that supports from the rear surface of the case 60. Therefore, the case 60 and the EMI shielding filter 46 of the glass type front filter 40 are both earthed to a ground voltage, and absorb electromagnetic waves emitted from the PDP 30 and discharge them. This is how the emission of the electromagnetic waves to outside is blocked.
Lastly, the cover 70 encompasses the outside of the glass type front filter 40, and is connected to the case 60.
As discussed above, the related art PDP set includes the glass type front filter 40 for shielding electromagnetic waves and correcting optical characteristics. However, because the glass type front filter 40 includes a glass substrate made from the reinforced glass, which is relatively thick, the thickness and weight of the PDP set were increased, and the cost of manufacture was also increased.
As an attempt to solve the above-described problems, a film type front filter without a glass substrate, as shown in FIG. 4, has been suggested. The film type front filter 65 shown in FIG. 4 includes a color correcting film 68, a NIR blocking film 66, an EMI shielding filter 64, and an antireflection layer 62, each being sequentially adhered to an upper plate 15 of the PDP 30.
The antireflection coating 62 prevents incident light rays from outside from being reflected back to the outside. The EMI shielding filter 64 absorbs electromagnetic waves generated from the PDP 30, and shields the emission of the electromagnetic waves to outside. The NIR blocking film 66 absorbs near infrared rays that are generated from the PDP 30, and blocks the emission of the near infrared rays to outside. The color correcting film 68 contains a color dye, which is used to adjust or correct colors, whereby color purity can be improved. These films 62, 64, 66, and 68 are adhered to the PDP 30 through an adhesive or glue.
Both the glass type front filter 40 of FIG. 3 and the film type front filter 65 include an EMI shielding filter 46 or 64 for shielding EMI from the PDP 30. As shown in FIGS. 5 and 6, the EMI filter 46 or 64 includes an EMI shielding layer 75 formed of conductive meshes 74 and frames 72 for supporting the conductive meshes 74, and a base film 75 formed on the EMI shielding layer 75.
Referring to FIGS. 5 and 6, to form the conductive meshes 74 and the frames 72 a metal layer made from silver (Ag) or copper (Cu) for example undergoes photolithography and etching processes to be patterned. To be more specific, a metal foil is formed on the base film 76, and the metal foil is coated with a photoresist. Later, the photoresist coating is patterned by using a mask and thus, the frame and a photoresist pattern in mesh type are formed. The metal foil is patterned by using the photoresist pattern as a mask, and as a result, the EMI shielding layer 75 including the frames 72 and the conductive meshes 74 is formed on the base film 76, as illustrated in FIG. 6. Any photoresist patterns remaining on the frames 72 and the conductive meshes 74 are removed through a strip process.
The EMI shielding layer 75, namely the conductive meshes 74 and the frames 72, of the related art EMI shielding filter 46 or 64 is usually made from highly lustrous metals. Thus, an externally incident lights R1 or display lights R2 emitted from the PDP 30 are reflected by the metallic conductive meshes 74 and frames 72. These reflected lights by the EMI shielding filter 75 increases overall black level or brightness of the PDP 30, resulting in deterioration of contrast ratio.